There's a lot in here.
Yes, radiotherapy can have side effects. However, side effects impacting urinary or rectal quality of life happen in around 5% of cases - you should ask the radio oncologist what that figure is for people with your diagnosis and treatment plan. With such a low disease burden, you might be interested in Brachytherapy (internal radiotherapy) too if suitable. As for bowel cancer, prostate radiotherapy may double your risk of this in around 20 years time. However, we obviously only have data from those who had radiotherapy 20 years ago, and it's probably a reasonable assumption that with today's much more accurately delivered radiotherapy, the incidence for those being treated today may be lower.
Prostatectomy does seem to cause more issues with urinary continence and erectile function, although these can happen with any of the prostate treatments. Of note is the impact is immediate after the prostatectomy and will hopefully recover (never quite as good as it was beforehand), whereas with radiotherapy, the impact (if any) is usually delayed and progresses slowly (plus some temporary impact during treatment). It's important to understand if you are likely to be able to have nerve sparing surgery when making the decision, although the surgeon won't know for sure until they're doing the op.
You don't want to plan on having a salvage prostatectomy after any other treatment, as the outcomes in terms of quality of life are never as good as having prostatectomy as your primary treatment, but it is possible - there are a few surgeons who specialise in it, but most won't be able to do it, so you would be referred to a specialist centre. Having said that, recurrence in the target radiotherapy area is quite rare - when you get recurrence after radiotherapy, it's usually because the cancer was already somewhere else when you were treated, and a prostatectomy would have failed for the same reason. Radiotherapy is avoided if possible for younger patients, but if you live for a long time after radiotherapy, then the chance of recurrence in the target area from new cancer formation may be increase. TURPs are sometimes done first in order to do radiotherapy (and this would be even more important for brachytherapy). If you have flow problems or other problems related to an enlarged prostate, this might be an additional factor to consider a prostatectomy, because it should solve those problems, which the other treatments won't do long term, and you'd probably still need a TURP in the future.
If you are interested in a focal therapy (such as HIFU, Cryotherapy, Nanoknife), then you need to get an opinion from a focal therapy centre, and I wouldn't take much notice of clinicians not involved in the treatment. Yes, it needs good imaging, usually better than many hospitals do, so they often end up doing their own imaging rather than relaying on that which has already been done. Also be clear if the focal therapy is with curative intent or with the intent of putting you back on to active surveillance afterwards which is often done if they decide to only treat the major cancers and leave minor ones.